The invention relates to the field of metallurgy, rolling production and is meant, in particular for manufacturing intermediate and final products of zirconium alloys.
The known method of the production of zirconium alloy items (RU Patent No. 2,037,555, C22F/18, 1995.), includes hot deformation of the billet, preliminary cold deformation and vacuum annealing at 560-590xc2x0 C. with the isothermic time interval of 3 to 4 hours , cold rolling with 17 to 31% of the degree of deformation at the last passing and subsequent final vacuum annealing at 560-585xc2x0 and isothermic time interval of 5 to 7 hours.
Technique which conforms the closest with the present application includes the following sequence of operations: the manufacturing of an ingot, its preliminary xcex2-processing, the production of a billet by means of hot molding at the temperature of xcex1-zirconium existence, the annealing of the billet at the temperature of 380 to 650xc2x0, the cold deformation of the billet with intermediate annealings at the temperature of xcex1-zirconium existence and finishing of the billet to get the ready product (US. Pat. No. 4,649,023, CI. C22C 16/00, 1987.), as well as the method differing from the above mentioned by the following peculiarities:
after xcex2-processing before hot molding of the ingot the billet is annealed at the temperature of 380xc2x0 C. to 650xc2x0 C.:
before the annealing after the hot molding the billet is treated by quenching at the temperature of 920xc2x0 C. to 1070xc2x0 C., the said annealing being performed at the temperature of 380xc2x0 C. to 520xc2x0 C.;
the quenching is performed at the rate of 60xc2x0 C./s to 1000xc2x0 C./s (RU Patent No. 2,032,760, C22F 1/18, 1995.).
It is well-known in the art that zirconium alloy tubes of the final size are produced by means of the cold rolling from the specially manufactured thick-wall tube intermediate product having high performance mechanical properties and precise geometric dimensions , which is termed SUPER-TREX or TREX in foreign references (E. Ross Bradley and George P. Sabol , editors. Zirconium in the Nuclear Industry: Eleventh International Symposium ASTM Publication Code Number (PCN): 04-012950-04 ASTM 100 Barr Harbor Drive West Conshohocken, Pa. 19428-2959). The geometric dimensions of the most common intermediate products are 63.5xc3x9710.9 mm, 44.5xc3x977.62 mm.
There is a known method of production of cladding tubes from zirconium alloys with the use of intermediate products 63.5xc3x9710.9 and 44.5xc3x977.62 mm, this method allowing only produce high-quality cladding tubes with the degree of deformation 51% after one cold rolling pass, the value of 80% resulting in the formation of numerous cracks (FR Patent No. 2,584,097, 1987. C22 F I/18:c22 16/00.).
The applied invention solves the task of the improvement of quality of zirconium alloy articles by the provision of deformation conditions without the disturbance of the continuity of the material of articles, obtaining the uniform metal structure along and across the articles and the improvement of technical and economic factors of their production by means of the increase of the dimensions of the initial billets and the improvement of the quality of tube intermediate products.
The outlined aim is achieved by the fact that for manufacturing tubes and intermediate tube intermediate products of SUPER-TREX, TREX and binary zirconium alloys in addition to the previously known operations:
manufacturing of an ingot,
its preliminary xcex2-deformation processing before the production of the initial billet,
manufacturing of the tubular billet by means of hot molding of the initial billet at the temperature of the existence of xcex1-zirconium,
cold deformation of the tubular billet with intermediate annealings at the temperature of the existence of xcex1-zirconium,
finishing of the billet to get the ready article.
The cold deformation of tubes is performed at the total reduction of xcexcxcexa3 greater than 100 for manufacturing ready articles or xcexcxcexa3 less than 50 for manufacturing tubular intermediate products of SUPER-TREX, TREX TYPES, the reduction being xcexc less than 2.0 at the first stage of tube rolling, and the final tube annealing is performed at the temperature of the existence of xcex1-zirconium, and xcexc=Sbillet/Stube where Sbillet is the cross section area of the rolling billet, Stube is the cross section of the rolled tube;
xcexc=Sinit. billet/Sready tube where Sinit. billet is the area of the cross section of the billet for the first rolling, Sready tube is the area of the cross section of the ready tube after the last rolling.
In case it is necessary to get the final size tubes or intermediate products of SUPER-TREX, TREX types of multi-component zirconium alloys or binary zirconium alloys, when it is necessary to get the articles of the improved quality (with the orientation of hydrides Fn less than 0.3 in any portion of the tube, stable texture and/or other requirements), in addition to the operations mentioned in the first variant of the claimed method, after hot molding at the temperature of the existence of xcex1- or (xcex1+xcex2)-zirconium, the tubular billet is annealed at the temperature exceeding by 30 to 60xc2x0 C. the temperature of transition of the alloy from the intermediate (xcex1+xcex2) phase to xcex2-phase zirconium, the mechanical processing and the subsequent tempering-of the quenched billet at the temperature of the existence of xcex1-zirconium.
The conducting of cold rolling of tubes at the total reduction of xcexcxcexa3 greater than 100, by means of a higher degree of metal working allows to get the ready articles with the uniform structural condition in length and cross section.
The suggestion limitation of the reduction value at the first stage of rolling results in the decrease of shearing stresses occurring during the deformation of billets in cold rolling nulls well below the values of the tensile strength of zirconium alloys having been exposed to the above mentioned thermal treatment, both multi0component and more plastic, binary ones, resulting in the deformation of the alloys without disturbance of the continuity. At the subsequent stages of rolling the reduction is increased due to the rise of the plasticity of the alloys after the first state of rolling and the subsequent annealing. In case of the manufacturing of the tubular intermediate products of SUPER-TREX or TREX types the total reduction during the cold rolling can be xcexcxcexa3 less than 50 (because the intermediate products are usually manufactured in 1 to 3 passing cold rolling as distinct from the final size tubes for which the number of passings can be as much as 5 to 8 and taking into account limitations of reduction at the first stage of the cold rolling xcexc less than 2.0).
The conducting of the quenching of tubular billets after the hot molding at the temperature exceeding by 30 to 60xc2x0 C. the temperature of transition of the alloy from the intermediate (xcex1+xcex2) phase to the xcex2-phase of zirconium, mechanical processing and tempering of the quenched billet at the temperature of the existence of xcex1-zirconium provides the complete phase recrystallization of the alloys and their transformation into the structural condition of martensite type with fine-grained (grain size being 0.16 to 0.22 mm) macrostructure and with the maximum dispersion of intermetallic and admixture phases with the fixation of admixture and alloy components in the satiated solid solution (FIG. D). Besides the thermal treatment provides more than twofold reserve of the alloy plasticity for the first stage of the cold rolling as compared with the previous method (Table on page 9), and in the combination with the limitation of the reduction value during the first stage of the cold rolling it predetermines the conducting of the cold deformation without micro- and macrofailures (FIG. 2). The claimed deformation and thermal treatment allow to obtain the uniform structure in length and cross section of the pressed billet (FIG. 4). In previous methods the pressed billet has non-uniform structure in length and cross section (FIG. 3) due to peculiarities of the process of direct pressing (I. L. Perlin, L. H. Reitbarg. Theory of Metal Pressing. Moscow. Metallurgy, 1975, p. 350), which is inheritedly maintained up to the production of the tubes of final size. Machining of the quenched tubular billet provides the removal of the superficial oxidized and saturated with gas layer which is formed after the quenching and simultaneously it allows to remove defects on the outer and inner surfaces of the billet which appear in the process of the hot molding. The improvement of the quality of the billet surface allows to avoid the deterioration of plastic properties of the metal (G. V. Filimonov, NikishovPilgering of Zirconium Tubes, Moscow, Metallurgy, 1988, p. 26) and to exclude the conditions of the disturbance of continuity due to the superficial defects during the subsequent cold deformation.